Abstract
By combining kinetics and theoretical calculations, we show here the benefits of going beyond the concept of static localized and defined active sites on solid catalysts, into a system that globally and dynamically considers the active site located in an environment that involves a scaffold structure particularly suited for a target reaction. We demonstrate that such a system is able to direct the reaction through a preferred mechanism when two of them are competing. This is illustrated here for an industrially relevant reaction, the diethylbenzene–benzene transalkylation. The zeolite catalyst (ITQ-27) optimizes location, density, and environment of acid sites to drive the reaction through the preselected and preferred diaryl-mediated mechanism, instead of the alkyl transfer pathway. This is achieved by minimizing the activation energy of the selected pathway through weak interactions, much in the way that it occurs in enzymatic catalysts. We show that ITQ-27 outperforms previously reported zeolites for the DEB-Bz transalkylation and, more specifically, industrially relevant zeolites such as faujasite, beta, and mordenite.
Highlights
Production of alkylaromatics is a crucial process in the modern chemical industry since they are well-established precursors for many important intermediates and chemicals.[1−3] Ethylbenzene (EB) is one of the industrial alkylaromatics with a higher production capacity worldwide, which is mostly consumed in the manufacture of polystyrene.[4]
Based on the above exposed premises, the DPDMP+ mimicking the diaryl intermediates involved in the DEB-Bz transalkylation mechanism was used as organic structuredirecting agents (OSDAs), and the synthesis resulted in the selective crystallization of the ITQ-27 zeolite with the IWV framework
The DEB-Bz transalkylation activity of IWV-M was tested in a fixed bed continuous reactor in gas as well as in the liquid phase and compared with that of catalysts currently employed in industry such as faujasite (FAU), beta (*BEA), MCM-22 (MWW), and mordenite (MOR).[9,10,12−14]
Summary
Production of alkylaromatics is a crucial process in the modern chemical industry since they are well-established precursors for many important intermediates and chemicals.[1−3] Ethylbenzene (EB) is one of the industrial alkylaromatics with a higher production capacity worldwide, which is mostly consumed in the manufacture of polystyrene.[4]. Diethylbenzene transalkylation can proceed through two main reaction pathways (Scheme 1).[15,16,25,17−24] The alkyl transfer mechanism (Scheme 1a) involves consecutive dealkylation and alkylation steps that proceed through unstable pentacoordinated carbonium ion intermediates.[16,26] The first dealkylation of DEB produces an EB molecule and a surface ethoxy group that, in a second step, reacts with benzene and yields EB. The ethoxy group can react with EB or DEB molecules present in the zeolite channels to form undesired overethylated byproducts such as DEB and triethylbenzene (TEB).[27] In addition, the surface ethoxy can decompose into ethene and regenerate the Brønsted acid site, further decreasing the yield of EB
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